How to render LINE particles in cycles render?
As of Blender 2.82, Cycles only renders Objects and Collections as particles (Blender docs link here)

However, here's a solution that might be helpful.

You can create an object shaped like a line (a long rectangle):


And then use it as the Object your particle system is rendered as. Set the rotation to orient along the velocity, and make sure to check "Dynamic" in the rotation section so it updates the rotation as the particles move or bounce.


Here's a quick view of what that generates:


Hope that helps someone Googling this in the future-